High-energy Colliders Research Articles

Linear colliders based on laser-plasma accelerators

Laser-plasma accelerators are capable of sustaining accelerating fields of 10–100 GeV/m, 100–1000 times that of conventional technology and the highest fields produced by any of the widely researched advanced accelerator concepts. Laser-plasma accelerators also intrinsically accelerate short particle bunches, several orders of magnitude shorter than that of conventional technology, which leads to reductions in beamstrahlung and, hence, savings in the overall power consumption to reach a desired luminosity. These properties make laser-plasma accelerators a promising accelerator technology for a more compact, less expensive high-energy linear collider providing multi-TeV polarized leptons. In this submission to the Snowmass 2021 Accelerator Frontier, we discuss the motivation for a laser-plasma-accelerator-based linear collider, the status of the field, and potential linear collider concepts up to 15 TeV. We outline the research and development path toward a collider based on laser-plasma accelerator technology, and highlight near-term and mid-term applications of this technology on the collider development path. The required experimental facilities to carry out this research are described. We conclude with community recommendations developed during Snowmass.

Footprints of New Physics in the angular distribution of [formula omitted] decays

We investigate the angular decay distribution of the four-fold Bc→Ds⁎(→Dsγ)μ+μ−, and Bc→Ds⁎(→Dsπ)μ+μ− decays that proceed through b→sμ+μ− quark level transition. We use the model independent effective Hamiltonian with vector and axial vector new physics operators to formulate the angular observables and study the implications of different latest new physics scenarios, taken from the global fits to all the b→s data, on these observables. We also give Standard Model and new physics predictions of several observables such as differential branching ratios, forward backward asymmetry, longitudinal polarization fraction of Ds⁎, and the unpolarized and polarized lepton flavor universality violating ratios. Future measurements of the predicted angular observables, both at current and future high energy colliders, will add to the useful complementary data required to clarify the structure of new physics in b→sℓℓ neutral current decays.

Lightest Higgs boson decays h → MZ in the μ from ν supersymmetric standard model

We study the lightest Higgs boson decays h → MZ in the μ from ν supersymmetric standard model (μνSSM), where M is a vector meson (ρ, ω, ϕ, J/Ψ, Υ). Compared to the minimal supersymmetric standard model (MSSM), the μνSSM introduces three right-handed neutrino superfields, which lead to the mixing of the Higgs doublets with the right-handed sneutrinos. The mixing affects the lightest Higgs boson mass and the Higgs couplings. In suitable parameter space, the μνSSM can give large new physics (NP) contributions to the signal strengths of h → MZ and h → γγ, which may be detected by a 100 TeV collider or the other future high energy colliders.

Heavy neutral leptons at muon colliders

The future high-energy muon colliders, featuring both high energy and low background, could play a critical role in our searches for new physics. The smallness of neutrino mass is a puzzle of particle physics. Broad classes of solutions to the neutrino puzzles can be best tested by seeking the partners of SM light neutrinos, dubbed as heavy neutral leptons (HNLs), at muon colliders. We can parametrize HNLs in terms of the mass mN and the mixing angle with ℓ-flavor Uℓ. In this work, we focus on the regime mN> O(100) GeV and study the projected sensitivities on the |Uℓ|2 − mN plane with the full-reconstructable HNL decay into a hadronic W and a charged lepton. The projected reach in |Uℓ|2 leads to the best sensitivities in the TeV realm.

Associated Higgs boson production with Z boson in the minimal U(1)X extended Standard Model

The minimal U(1)X extension of the Standard Model (SM) is a simple and well-motivated extension of the SM, which supplements the SM with the seesaw mechanism for naturally generating the light neutrino masses and offers various interesting phenomenologies. In the model, the U(1)X charge of each SM field is characterized by the U(1)X charge of the SM Higgs doublet with a free parameter xH. Due to the U(1)X charge of the Higgs doublet, the Higgs boson has a trilinear coupling with the Z boson and the U(1)X gauge boson (Z′). With this coupling, a new process for the associated Higgs boson production with a Z boson arises through a Z′ boson in the s-channel at high energy colliders. In this paper, we calculate the associated Higgs boson production at high energy colliders and show interesting effects of the new Z′ boson mediated process, which can be tested in the future.

Revealing the origin of neutrino masses through the Type II Seesaw mechanism at high-energy muon colliders

The future muon collider can play as an ideal machine to search for new physics at high energies. In this work, we study the search potential of the heavy Higgs triplet in the Type II Seesaw mechanism at muon colliders with high collision energy and high luminosity. The latest neutrino oscillation data are taken into account for realizing the leptonic decay modes of the charged Higgs bosons (H±±, H±) in the Type II Seesaw. We show the impact of neutrino mass and mixing parameters on the purely leptonic decays. The pair production of doubly charged Higgs H++H−− is through direct μ+μ− annihilation and vector boson fusion (VBF) processes at muon collider. The associated production H±±H∓ can only be induced by VBF processes. We simulate both the purely leptonic and bosonic signal channels of charged Higgs bosons in Type II Seesaw, together with the Standard Model backgrounds. We show the required luminosity for the discovery of the charged Higgses and the reachable limits on the leptonic decay branching fractions.

Flavor changing interactions confronted with meson mixing and hadron colliders

We have witnessed some flavor anomalies appearing in the past years, and explanations based on extended gauge sectors are among the most popular solutions. These beyond the Standard Model (SM) theories often assume flavor-changing interactions mediated by new vector bosons. Still, at the same time, they could yield deviations from the SM in the ${K}^{0}\ensuremath{-}{\overline{K}}^{0}$, ${D}^{0}\ensuremath{-}{\overline{D}}^{0}$, ${B}_{d}^{0}\ensuremath{-}\overline{B}{{\text{ }}^{0}}_{d}$, and ${B}_{s}^{0}\ensuremath{-}\overline{B}{{\text{ }}^{0}}_{s}$ meson systems. Using up-to-date data on the mass difference of these meson systems, we derive lower mass bounds on vector mediators for two different parametrizations of the quark mixing matrices. Focusing on a well-motivated model based on the fundamental representation of the weak SU(3) gauge group, we put our findings into perspective with current and future hadron colliders to conclude that meson mass systems can give rise to bounds much more stringent than those from high-energy colliders and that recent new physics interpretations of the $b\ensuremath{\rightarrow}s$ and $R({D}^{*})$ anomalies are disfavored.

Modeling of three-dimensional betatron oscillation and radiation reaction in plasma accelerators

Betatron oscillation is a commonly known phenomenon in laser or beam driven plasma wakefield accelerators. In the conventional model, the plasma wake provides a linear focusing force to a relativistic electron, and the electron oscillates in one transverse direction with the betatron frequency proportional to $1/\sqrt{\gamma}$, where $\gamma$ is the Lorentz factor of the electron. In this work, we extend this model to three-dimensional by considering the oscillation in two transverse and one longitudinal directions. The long-term equations, with motion in the betatron time scale averaged out, are obtained and compared with the original equations by numerical methods. In addition to the longitudinal and transverse damping due to radiation reaction which has been found before, we show phenomena including the longitudinal phase drift, betatron phase shift and betatron polarization change based on our long-term equations. This work can be highly valuable for future plasma based high-energy accelerators and colliders.

Heavy neutral leptons at the Electron-Ion Collider

The future Electron-Ion Collider (EIC) at Brookhaven National Laboratory, along with its primary capacity to elucidate the nuclear structure, will offer new opportunities to probe physics beyond the Standard Model coupled to the electroweak sector. Among the best motivated examples of such new physics are new heavy neutral leptons (HNLs), which are likely to play a key role in neutrino mass generation and lepton number violation. We study the capability of the EIC to search for HNLs, which can be produced in electron- proton collisions through charged current interactions as a consequence of their mixing with light neutrinos. We find that, with the EIC design energy and integrated luminosity, one is able to probe HNLs in the mass range of 1 – 100 GeV with mixing angles down to the order of 10−4 − 10−3 through the prompt decay signatures, and in the mass range of 1 10 GeV with |Ue|2 ~ 10−6 – 10−4 via the displaced decay signatures. We also consider the invisible mode where an HNL is undetected or decaying to dark sector particles. One could potentially probe heavy HNLs for mixing angles in the window 10−3 – 10−2, provided SM background systematics can be brought under control. These searches are complementary to other probes of HNLs, such as neutrino-less double-β decay, meson decay, fixed-target, and high-energy collider experiments.

Investigation of Z-boson decay into and baryons within the NRQCD factorization approach* *Supported in part by the Natural Science Foundation of China (12265010) and the Project of Guizhou Provincial Department of Education (KY[2021]030)

Z-boson decay provides a good opportunity to search for the baryon because a large number of its events can be collected at high energy colliders. In this paper, we perform a complete investigation of the indirect production of the and baryons via the Z-boson decay process with a quark under the NRQCD factorization approach. After considering the contribution from the diquark states , , , and , the calculated branching fractions are and . Furthermore, the and production events are predicted to be of the order of and at the LHC collider, and the order of and for the CEPC collider. We then estimate the production ratio for with in Z-boson decay, that is, and , respectively. Finally, we present the differential decay widths of and with respect to and z distributions and analyze the uncertainties.

The unseen: revealing the blind production procedure and experience for NP data

A unique experiment was conducted by the STAR Collaboration in 2018 to investigate differences between collisions of nuclear isobars, a potential key to unraveling one of the physics mysteries in our field: why the universe is made predominantly of matter. Enhancing the credibility of findings was deemed to hinge on blinding analyzers from knowing which dataset they were examining, necessitating efforts by the data production team to investigate and implement new (in our field) blinding practices. With nearly two decades of established machinery intended to provide open data and metadata access in STAR, the breadth of details to consider for a successful blinding process was substantial.In this paper, we will review the experience of the first-ever species-blind data production in high energy collider physics. Considerations of what needed blinding, how to blind it, and from whom, will be discussed. Practical impositions on the selection of data to produce and how to produce it will also be highlighted as tell-tales can arise even where there were operational efforts to avoid them. With the appropriate blinding achieved, analyzers and reviewers have been empowered to focus on the physics of interest.

Analyzing N-Point Energy Correlators inside Jets with CMS Open Data.

Jets of hadrons produced at high-energy colliders provide experimental access to the dynamics of asymptotically free quarks and gluons and their confinement into hadrons. In this Letter, we show that the high energies of the Large Hadron Collider (LHC), together with the exceptional resolution of its detectors, allow multipoint correlation functions of energy flow operators to be directly measured within jets for the first time. Using Open Data from the CMS experiment, we show that reformulating jet substructure in terms of these correlators provides new ways of probing the dynamics of QCD jets, which enables direct imaging of the confining transition to free hadrons as well as precision measurements of the scaling properties and interactions of quarks and gluons. This opens a new era in our understanding of jet substructure and illustrates the immense unexploited potential of high-quality LHC data sets for elucidating the dynamics of QCD.

Shining light on magnetic monopoles through high-energy muon colliders

The search for magnetic monopoles has been a longstanding concern of the physics community for nearly a century. However, up to now, the existence of elementary magnetic monopoles remains an open question. The electroweak 't Hooft-Polyakov monopoles have been predicted with mass at the order of 10 TeV. This mass scale is unreachable at current colliders. Recently, the muon colliders have gained much attention in the community due to technological developments. The advantages of the muon beam encourage us to raise the high-energy option and consider the high-energy muon collider as a unique opportunity to search for magnetic monopoles. This letter discusses the production of magnetic monopoles via the annihilation process and proposes the search for magnetic monopoles at future high-energy muon colliders.

Interplay between resonant leptogenesis, neutrinoless double beta decay and collider signals in a model with flavor and CP symmetries

We present a low-scale type-I seesaw scenario with discrete flavor and CP symmetries. This scenario not only explains the measured values of the lepton mixing angles, but also makes predictions for leptonic CP violation, and connects the low-energy CP phases relevant for neutrino oscillation and neutrinoless double beta decay experiments with the high-energy CP phases relevant for leptogenesis. We show that the three right-handed Majorana neutrinos in this scenario have (almost) degenerate masses and their decays can explain the observed baryon asymmetry of the Universe via resonant leptogenesis. We study the correlation of the predicted baryon asymmetry with lepton-number-violating signals at high-energy colliders, including both prompt and displaced vertex/long-lived signatures, as well as in low-energy neutrinoless double beta decay experiments. We find that the normal ordering of light neutrino masses leads to an enhanced collider signal, whereas the neutrinoless double beta decay provides a promising probe in the inverted ordering case.

Neutron star observations of pseudoscalar-mediated dark matter

Scattering interactions between dark matter and Standard Model states mediated by pseudoscalars are generically challenging to uncover at direct detection experiments due to rates suppressed by powers of the local dark matter velocity ${v}_{\mathrm{DM}}\ensuremath{\sim}{10}^{\ensuremath{-}3}c$. However, they may be observed in the dark matter-induced heating of neutron stars, whose steep gravitational potentials prevent such suppression by accelerating infalling particles to semirelativistic speeds. We investigate this phenomenon in the context of two specific, self-consistent scenarios for pseudoscalars coupled to dark matter, and compare the sensitivity of neutron star heating to bounds from direct searches for the mediators and dark matter. The first ``lighter'' scenario consists of sub-10 GeV mass dark matter mediated by an axionlike particle, while the second ``heavier'' scenario has dark matter above 10 GeV mediated by a dark pseudoscalar that mixes with a pseudoscalar from a two-Higgs doublet (the so-called $2\mathrm{HDM}+a$ model). In both frameworks, we show that imminent measurements of neutron stars will be able to test pseudoscalar-mediated dark matter beyond the reach of direct dark matter searches as well as bounds on the mediators from flavor observables, beam dump experiments, and high-energy colliders.

Distinguishing two dark matter component particles at e+e− colliders

We investigate ways of identifying two kinds of dark matter (DM) component particles at high-energy colliders. The strategy is to notice and distinguish double-peaks(humps) in the missing energy/transverse energy distribution. The relative advantage of looking for missing energy is pointed out, in view of the fact that the longitudinal component of the momentum imbalance becomes an added input. It thus turns out that an electron-positron collider is better suited for discovering a two-component DM scenario, so long as both of the components are kinematically accessible. This and a number of associated conclusions are established, using for illustration a scenario including a scalar and a spin-1/2 particle. We also formulate a set of measurable quantities which quantify the distinguishability of the two humps, defined in terms of double-Gaussian fits to the missing energy distribution. The efficacy of these variables in various regions of the parameter space is discussed, using the aforesaid model as illustration.

Family nonuniversal Z′ effects on Bd,s→K*0K¯*0 decays in perturbative QCD approach

The nonleptonic decays ${B}_{d,s}\ensuremath{\rightarrow}{K}^{*0}{\overline{K}}^{*0}$ are reanalyzed in perturbative QCD approach, which is based on the ${k}_{\mathrm{T}}$ factorization. In the Standard Model, the calculated branching fraction and longitudinal polarization fraction of ${B}_{d}\ensuremath{\rightarrow}{K}^{*0}{\overline{K}}^{*0}$ are in agreement with experimental measurements, while the predictions of ${B}_{s}\ensuremath{\rightarrow}{K}^{*0}{\overline{K}}^{*0}$ cannot agree with data simultaneously. The parameter that combines longitudinal polarization fractions and branching fractions is calculated to be ${L}_{{K}^{*}{\overline{K}}^{*0}}^{\mathrm{PQCD}}={12.7}_{\ensuremath{-}3.2}^{+5.6}$, which is also larger than that extracted from experimental measurements. We then study all observables by introducing a family nonuniversal ${Z}^{\ensuremath{'}}$ boson in $b\ensuremath{\rightarrow}sq\overline{q}$ transitions. In order to reduce the number of new parameters, we simplify the model as possible. It is found that with the fixed value ${\ensuremath{\omega}}_{{B}_{s}}=0.55$, these exists parameter space where all measurements, including the branching fraction, longitudinal polarization fraction, and ${L}_{{K}^{*}{\overline{K}}^{*0}}$-parameter, could be accommodated simultaneously. All our results and the small parameter space could be further tested in the running LHC experiment, Belle-II, and future high-energy colliders.

Single production of vectorlike B quarks decaying into bh at the CLIC

New vectorlike quarks have been predicted in many scenarios of new physics beyond the Standard Model, which may be potentially discovered at the current and future high-energy colliders. Based on a model-independent framework, we study the single production process of the doublet vectorlike B-quark (VLQ-B) at the future Compact Linear Collider (CLIC) and explore the possible signals through the decay channel B→bh with subsequent decay mode of the Higgs boson: h→WW⁎→ℓνjj. By performing a rapid detector simulation of the signal and background events as well as considering the initial state radiation and beamstrahlung effects, the exclusion limit at the 95% confidence level and the 5σ discovery reach in the parameter spaces (the coupling strength κB and the VLQ-B mass) are obtained at the future 3 TeV CLIC with an integrated luminosity of 5 ab−1.

Pair production of the vectorlike top partner at future muon collider

Motivated by the recent interests in future high-energy muon colliders, we study the search potential of heavy singlet vectorlike top partner (VLQ-T) through the s-channel process μ+μ−→TT¯ at such facilities with s=6 TeV. We focus on the final signals via the T→Wb decay channel where one of the W bosons decays leptonically and the other decays hadronically. By carrying out a full simulation for the signals and the relevant Standard Model backgrounds, the 2σ exclusion limit and 5σ discovery prospects are, respectively, obtained on the VLQ-T mass and the branching ratio of T→Wb. The numerical results show that the future high-energy muon collider will be a promising hunting ground for such new particles.

Quantum annealing for jet clustering with thrust

Quantum computing holds the promise of substantially speeding up computationally expensive tasks, such as solving optimization problems over a large number of elements. In high-energy collider physics, quantum-assisted algorithms might accelerate the clustering of particles into jets. In this study, we benchmark quantum annealing strategies for jet clustering based on optimizing a quantity called "thrust" in electron-positron collision events. We find that quantum annealing yields similar performance to exact classical approaches and classical heuristics, but only after tuning the annealing parameters. Without tuning, comparable performance can be obtained through a hybrid quantum/classical approach.